The film forming method and the surface reforming method based on low-pressure glow discharge plasma are widely known and industrially applied in various areas. It is also known that one of the surface treatment methods with low-pressure glow discharge plasma is that known as the organic plasma reaction method for forming a thin film and/or reforming the surface by means of the conversion an organic compound gas into plasma.
There are available, for example, a method of plasma-exciting a hydrocarbon gas in a vacuum vessel and forming by precipitation an amorphous carbon film on a silicon substrate or a glass substrate, and a method for forming a plasma polymer film of an unsaturated hydrocarbon such as ethylene.
However, all these conventional surface treatment methods based on low-pressure glow discharge plasma require an apparatus and facilities for creating low-pressure conditions because the reaction is to take place under a vacuum of about 1.times.10.sup.-5 to 1.times.10.sup.-3 torr in all cases, thus resulting in complicated operations and maintenance and a high manufacturing cost. A low-pressure method has another defect of a difficult treatment of a large-area substrate.
With a view to overcoming these defects in the conventional methods, the present inventor carried out extensive studies and completed a new film forming method based on glow discharge plasma under atmospheric pressure permitting reduction of costs for apparatus and facilities and easy film formation on a large-area substrate. The backdrop for this development included inventor's research on ozone producing silent discharge for many years and analysis of the reaction mechanism regarding plasma film formation.
The reaction caused by glow discharge under atmospheric pressure has been studied by the present inventor as a reaction of a fluorine-containing gas, and the present invention was a perfection of his study into a film forming method and further a surface reforming method.
Furthermore, the present invention provides a solution also to the weak point of glow discharge plasma reaction under atmospheric pressure of an easily producing arc discharge when the substrate is a conductive metal or alloy.
More specifically, the present invention provides an improved reaction method based on glow-discharge plasma under the atmospheric pressure which makes available, even with a metal or alloy substrate, a highly stable plasma of a reaction gas with a high reaction activity under atmospheric pressure.